Esophageal tubes, probes, balloons, and other devices have been used to monitor internal physiologic function, decompress all portions of the alimentary tract, and protect the airway in sedated patients undergoing surgical procedures. It is currently common medical practice to use a nasogastric tube in most patients requiring mechanical ventilation during surgical procedures, and to use a nasogastric tube to mark the anatomic relationships between the left atrium and the esophagus in patients undergoing atrial fibrillation ablation with general anesthesia and or conscious sedation procedures. Marking the esophagus during atrial fibrillation (left atrial) ablation has gained prominence because of the occurrence of unintended esophageal heat injury.
Various ablation techniques, such as high-energy microwaves, radiofrequency, and cryogenic methods, have been used to create a focal tissue lesion in the atrium to treat atrial dysrhythmias and atrial fibrillation. Common left atrial ablation techniques include wide circumferential lesions encircling the pulmonary veins and linear lesions on the posterior left atrium, mitral isthmus, and left atrium roof. The esophagus and posterior left atrial wall are located proximate to one another (see FIG. 1) and near the ablation zone for left atrial ablation and pulmonary vein isolation. Studies have shown that the mean length and width of the esophagus in contact with the posterior left atrium are 5.8 centimeters and 1.36 centimeters, respectively. Although most patients have a small fat pad separating the posterior left atrium and esophagus, this fat pad is often discontinuous. Due to the close proximity of the esophagus and the left atrium, ablation along the posterior left atrium may result in unintended thermal injury to the esophagus and subsequent fatal esophageal-atrial fistula presenting as a fatal complication 1-3 weeks following left atrial ablation. An esophageal-atrial fistula can cause an air embolism with a stroke, mediastinitis, GI bleeding, and have high mortality rates.
Different techniques have been used to monitor the temperature and position of the esophagus during ablation of the atrium. Strategies to avoid esophageal injury resulting from left atrial ablation include: avoidance of energy delivery at close esophageal atrial sites, decreased ablative energy and duration of energy delivery (time) at target sites, use of intracardiac echo and other imaging techniques to avoid unsafe ablative sites, and esophageal temperature monitoring to recognize esophageal heating. However, these precautionary approaches have proven to be unreliable and/or likely to compromise the ablation procedure.
The anterior wall of the esophagus is separated from the posterior wall of the left atrium and/or the proximal pulmonary vein by 0 to 4 millimeters of fat and the oblique sinus recess of the pericardium. The separation distance between the anterior wall of the esophagus and the posterior wall of the left atrium becomes even less during phases of peristalsis of the esophageal musculature. The esophagus is a mobile organ that allows movement and adjusts to thoracic and diaphragmatic motion independent of the heart. Esophageal mobility is limited to some degree by venous connections and drainage of the esophagus, azyis vein and loose attachments to the mediastinal connective tissue. As a result, static imaging techniques are inadequate to monitor the position of the esophagus due to the mobility of the esophagus. Thus, real-time imaging techniques, such as intracardiac echocardiography, may be more effective in monitoring the variable esophageal and left atrial anatomic relationship due to mobility and peristalsis of the esophagus.
An alternative approach to avoid injury to the esophagus has been to deflect the esophagus away from the ablation site, such as by moving the esophagus one centimeter or more from the ablation site. Transesophageal echo probes have been utilized in attempts to deflect or mobilize the retrocardiac portion of the esophagus away from ablation sites, but have had limited success due to the bulkiness of the device and the inability of the curved distal tip of the probe to effectively deflect the esophagus. Attempts to excessively mobilize the esophagus need to be avoided, but gentle and defuse intraluminal deflection of 0.5 to 3.0 cm is within the physiologic range.
Therefore, there is a need for a nasogastric tube for deflecting the retro-cardiac esophagus to reduce the incidence of thermal injury of the esophagus due to an ablation procedure. In addition, there is a need for techniques to monitor the esophagus during an ablation procedure to identify and avoid thermal injury to the esophagus. Additional applications include control of the esophagus during radio-therapy for lung tumors.